Download Potential Pathogen Growth in Water Heaters

Project 4379:
Research Needs for Opportunistic
Pathogens in Premise Plumbing:
Experimental Methodology,
Microbial Ecology and Epidemiology
Overview of Project, Drivers for Research and Outcomes
Marc Edwards, Amy Pruden (PI), Joe Falkingham
Pathogens of Concern
Pathogen
Disease(s)
Host Organism
Required?
Mode of Exposure
Legionella
pneumophila
Legionnaires’ disease or
Pontiac fever in children
Yes
Inhalation or aspiration
Pseudomonas
aeruginosa
Urinary tract infections, respiratory
infections, dermatitis, soft tissue
infections, bacteremia, bone and joint
infections, GI infections
No
Wound infection; other
modes of transmission
are unknown
Mycobacterium
avium
Pulmonary disease,
cervical lymphadenitis (children)
No
Inhalation or aspiration
Acanthamoeba
Acanthamoeba keratitis
No
Wound infection
Naegleria fowleri
Primary amebic meningoencephalitis
No
Nasal aspiration
2
Opportunistic Pathogens
Opportunistic pathogens in premise plumbing
are now the primary source of water-borne
infectious disease in developed countries
Per year: Up to 18,000 Legionnaire’s and
30,000 MAC cases
Biofilm, not fecal-associated
Immunocompromised people particularly at risk
Regulatory challenge- who’s responsibility?
N. fowleri
P.aeruginosa
L.pneumophila
Mycobacterium avium
complex (MAC)
Acanthamoeba
Practical Drivers and Opportunities
• Increased reporting/detection
• Increased susceptible populations
•
•
•
•
Main water distribution system upgrades
Premise plumbing upgrades
Green building/green devices
Energy sustainability links
These are all coming one
way or another…
5
Microbial Ecology of Residential
Hot Water Heater Systems:
Role of Hot Water System Type/Design on Factors
Influential to Pathogen Re-growth: Temperature,
Chlorine Residual, Hydrogen Evolution and Sediment
Randi Brazeau, Amy Pruden and Marc Edwards
October 4, 2013
Background
• Conventional Wisdom: Temperature is the Key
– WHO vs. US temperature setting
– 48 °C  typically closer to 42-45 °C
Pathogen Growth  Water Heater Type
– Stratification in Electric Water Heaters vs. Gas
(Lacroix, 1999)
– Pinellas County and CDC: Legionella incidence higher
in buildings with hot water recirculation (Moore, et
al., 2006)
Variables of Hot Water Premise Plumbing
that Can Lead to Pathogen Growth
• Volumes per Day (Goldner, 1999)
– Average range: 42 – 160 GPD
– Extreme high: 360 GPD
– Extreme low: vacation home
• Type of Water Heater
– Standard, Recirculation, On-Demand, Electric, Gas, Solar,
etc. etc. etc.
•
•
•
•
Temperature Setting
Anode Rod Type
Flow Velocity
Pipe Material
Experimental Design
Electric Water Heater
60 0C
H2
Anode
Corrosion
Biofilm
Growth
H2
Heating
Elements
Mg or Al
Anode Rod
Scale
Buildup
H2
H2
Biofilm
Formation:
Nutrients and
Energy for
Microbial
Growth
350
Mg(OH)3,
Al(OH)3,
Fe(OH)3, Solids
and Sorbed
Nutrients
Testing Conditions – By the
Numbers
High Use
Low Use
49 °C
• 54 gal/per/day
• 3.14 per/family
• 50 gal tank
•3
turnovers/day
• 8-hour
Stagnation
• 1/6 of High Use
• 25% turnover –
2 times daily
• 12-hour
Stagnation
• EPA
recommended
setting
• Minimize
scalding risk
60 °C
• WHO, Canada,
Australia,
others
• Control
pathogen
growth
48 °C and High Use
TOP
2
3
BOTTOM
RECIRC
50
Temperature (°C)
4
45
40
35
30
25
20
STAND
Temperature (°C)
50
NO
GROWTH
45
40
GROWTH
35
30
25
20
0.25
0.75
1.25
1.75
2.25
3.25
4.25
4.75
Time After Flush (hr)
5.75
6.75
7.75
Chapter 3: Internal Tank Temperature Results –
Volumes at Risk!
Water Heater Type
Storage Volume (Tank)
Below 46 °C
Per Day
High Use
(% Tank)
Tank setting
60 °C
49 °C
STAND
31
78
RECIRC
22
100
Dissolved Oxygen –
Legionella is a Microaerophile
Hydrogen Generation in Systems
2500
Hydrogen (ppm)
2000
1500
STAND
4 x more
H2!
6.5 x
1000
more
H2!
RECIRC
DEMAND
500
0
High Use
Low Use
0.2 mg C/mg H2 (Morton et al., 2005)
BOTTOM OF TANKS
2.0
TOTAL CHLORINE (MG/L)
1.8
STAND
@ 60 °C
1.6
1.4
STAND
@ 48 °C
1.2
1.0
1 mg/L
RECIRC
@ 60 °C
0.8
0.6
RECIRC
@ 48 °C
0.4
0.2
0.0
0
2
4
6
8
10
12
STAGNATION TIME SINCE FLUSHING (HR)
14
50
Temperature (°C)
45
Field
Test
DT = ~12 °C
40
35
30
Lab
Test
Temperature (°C)
25
45
43
41
39
37
35
33
31
29
27
25
DT = ~10 °C
RECIRC
@ 48 °C
STAND
@ 48 °C
0.0
2.0
4.0
6.0
8.0
10.0
Shower Time (min)
12.0
14.0
Short Circuiting
COLD WATER
MIXING!
WOULD
CHECK VALVE
PREVENT
THIS FROM
HAPPENING?
COLD WATER
BYPASSES
TANK
ENTIRELY!
Public Health Implications?
• Potentially getting water straight from BOTTOM
of tank
– Cooler temperatures
– More sediment
• Pathogen nutrients?
• Biofilm attachment?
– Pathogen rich?
• Reverse flow
– Increased sheering of biofilm?
AOC (food) Generation Mechanisms
Four Potential Mechanisms
1.
2.
3.
4.
Nitrification (Zhang et al. 2009)
H2 oxidation (Morton et al. 2005)
Sorption to Iron/Aluminum Sediments (Butterfield et al. 2002)
Organics leaching from pipe materials (PEX)
NH3 Cycling
Humic/AOC
Sorption
During Flow
NH3 NO3-
Organics
leaching from
pipe material
(PEX)
FLOW
H2
H2
H2
Biofilm
Rust/Iron Sediments
Pipe Wall
H2 Evolution
Photo Adapted from Edwards et al. 2006
AOC Generation Mechanisms
• H2 oxidizing bacteria
– Sacrificial anode (Al or Mg)
corrodes producing H2 gas
– Supports growth of hydrogen
oxidizing bacteria
– Typical Mg-anode: 44” long by
0.7” wide, 490g, 5 yr lifetime
• 160 µg C/L everyday
Photo Adapted from Edwards et al. 2006
Conclusions
• Temperature is important, but it is more
complicated than deciding on a set point
• Recirculating systems have more H2, less
chlorine, less oxygen, higher turbidity and
higher metals than standard systems
• Design and operation of hot water systems is
important for comfort and health
• Organic matter (food) can be generated in hot
water systems